To obtain adipic acid in a high yield by oxidizing hydroxycaproic acid and/or -caprolactone with oxygen or an oxygen-containing gas in the presence of a platinum group metal as a catalyst.

This method for producing adipic acid comprises oxidizing (A) hydroxycaproic acid and/or -caprolactone, preferably in a tank type reactor in the state of an about 1-40 wt.% aqueous solution, with (C) oxygen or an oxygen-containing gas, such as air, in the presence of (B) a platinum group metal, such as platinum, palladium, rhodium or ruthenium, as a catalyst under stirring. In the reaction, the component C is preferably used in an amount of ≥1 fold mole based on the component A. The component B is preferably used in an amount of 0.1-200 wt.% based on the component A, when the tank type reactor is used. The reaction is preferably usually carried out at a reaction temperature of 80-220°C.